Blog Category: Quantum computation

Many people have asked me why I decided to write a book. A better questions is: “When you realized that writing the book was going to be orders of magnitude harder and take much longer than you thought it would, what made you decide to continue writing the book?”

My co-author, Wolfgang Polak, and I recently received a book review of the sort that is the dream of every author. A dream review is, of course, positive. But more importantly, it praises the aspects of the book that were most important to the author – the reasons the author kept going after other books on the subject came out and the author had a more reasonable (but still too optimistic) estimate of the vast amount of effort it would take to finish it. (The review appeared in Computing Reviews, but is behind a paywall. Excerpts appear on the book’s Amazon and MIT press web pages.)

MIT press takes pride in their cover designs, but warns authors that “schedules rarely allow for individual consultation between designers and authors.” They do, however, ask authors to fill out a detailed questionnaire that includes questions asking for the authors’ thoughts with respect to a cover. It was the third question “What would you like the viewer to think or feel when they see the cover?” that prompted me to think that a fabric with abstract, colorful designs would suggest a “gentle” introduction to an abstract and colorful subject. Continue Reading

Frequently, particularly when searching for work related to possibly novel research ideas I or others at FXPAL have had, it is not easy to determine when to stop searching. This dilemma comes up any time anyone is searching for something we are not sure exists. After doing N searches, and finding nothing, how certain can we be that it isn’t there?

An unusual example of an existence search came up as I was doing background research for my review of N. David Mermin’s book Quantum Computer Science that was recently published in ACM SIGACT News. As part of the review, I wanted to give a sense for the extent that Mermin’s thoughts and writings have influenced scholarly and popular thought on quantum mechanics. I thought I remembered that he was the originator of the “Shut up and calculate” interpretation of quantum mechanics, but I wanted to fact check before putting it in my review. Would this search be a hard or easy one?Continue Reading

Most people have heard of no more than two quantum algorithms: Shor’s factoring algorithm and Grover’s search algorithm. For five years after Grover’s algorithm, no one discovered a significantly novel quantum algorithm, only variations on Shor’s and Grover’s algorithms were found. The first truly new quantum algorithms were discovered starting in 2001. Now there are many quantum algorithms found using a variety of approaches, though the applications remain restricted. My recent overview of quantum computing mentions many of these algorithms. Bacon and van Dam provide a more detailed, but still high level, view of these algorithms. They group the algorithms into four categories corresponding to different approaches: quantum random walks, wave packet scattering, finding hidden symmetries, and simulating quantum physics. I hope many of you will enjoy learning more about, in their words, “the benefits of … studying the notion of an algorithm through the perspective of the physical laws of the universe.”

Which research result excited you the most in the past year? We’re not asking for the one you thought most important, or the one that would be most exciting to everyone, but which one got you, personally, most excited.

I’ll start things off with a result that delighted me so much I went around smiling all day, only feeling sad that more people couldn’t appreciate it! The result, that appeared in twopapers almost simultaneously, is that some quantum states are too entangled to be able to compute one way. The result enchants me because it is surprising, fundamental, and related to topics close to my heart. Prior to these papers, the conventional wisdom held that more entanglement could only help quantum computation. It came as a complete surprise that it could hurt! Dave Bacon writes beautifully and succinctly about these startling results in his viewpoint, published in Physics, about the twopapers published together in Physics Review Letters 102 last May. Here I give an briefer account in order to explain why these result delighted me so much.

I hope the entry conveys the excitement of the field while eliminating some of the hype. It is focused on what is known about what quantum computers can and cannot do. It does not try to explain how they do what they do. (For that, my tutorial with Wolfgang Polak remains a good starting place.) While the entry discusses well known aspects of quantum computation, such as Shor’s algorithm, quantum key distribution, and quantum teleportation, it also discusses many lesser known results including more recent algorithmic results and established limitations on quantum computation. I had the pleasure of writing about some of my favorite topics in quantum computing, including purely classical results inspired by the quantum information processing point of view, the elegant cluster state model of quantum computation, and Aaronson’s suggestion that limits on computational power be considered a fundamental guiding principle for physical theories, much like the laws of thermodynamics.